2.1 Technical Field
The invention relates to mobile communication devices. More particularly, the invention relates to base station set up and soft handoff.
2.2 Related Art
Cellular base stations form an important part of wireless communications. Wireless base stations, known in the art, have processors along with wired and wireless receivers and transmitters that receive and transmit information between mobile stations and base station controllers. Mobile terminals use transmitters and receivers, as known in the art, to transmit and receive information to base stations. The average cell size for a cellular base station is between two and three km in diameter. As the number of cellular users increases, base stations become strained to keep up with the demand for bandwidth from new users. With the use of web-enabled phones and other communication devices connected to IP networks, greater amounts of information will need to flow through base stations to users' communication devices. With large cell sizes, an increasing amount of data transactions is placed on the base stations, causing bottlenecks in information flow as well as dropped calls or connections with users.
Further, additional strain will be placed on the base station controller that coordinates handoff between adjoining base stations. In GSM systems, for example, the interface between a base station controller (BSC) and a main switching center (MSC) (A-interface) is specified in the following GSM specifications: GSM 08.01, 0802, 0804, 0806 0808, and 0820. Also the interface between the BTS and the BSC (the Abis-interface) is specified in other GSM specifications. Other cellular systems, like CDMA, also use similar interfaces for handoff. All use centralized control. These were designed for macro sized base stations where handoff does not happen often because of the size of coverage areas. However, with handoffs occurring at a high rate, current interfaces show inability to handle high volume handoffs efficiently. This is because soft handoff requires the exchange of received or transmitted signals with adjacent base stations. These signals all need to be passed through the BSC or MSC, which may be located distant from the actual BSs and MTs, and need to handle all hand off requests. Furthermore, if the existing methods described above are applied directly over IP (Internet Protocol) networks, it will be difficult for a mobile station to synchronize the data it receives from multiple base stations during a handoff. This is because it will be difficult for an IP network to deliver data from a distant BSC or MSC via multiple BSs to a mobile station while still being able to meet the strict timing requirements for data synchronization at the mobile station. This is especially true when the network load is heavy. Loss of synchronization will lead to forced termination of handoff.
FIG. 12 shows base stations 1202, 1203, and 1204 being controlled by base station controller (BSC) 1201. If a mobile station travels from the area covered by base station 1202 to the area covered by the base station 1203, BSC 1201 will receive and coordinate the handoff requests between the various entities. All coordination involves BSC 1201. As the number of base stations increase, the load on the BSC 1201 will increase, creating another bottleneck for information flow.
One solution is to decrease the capacity of each base station while increasing the number of base stations. These base stations (also referred to as pico base stations) have a much smaller coverage area yet provide a greater effective bandwidth for receiving and transmitting large amounts of information. A difficulty in bringing online a new base station is the time required to properly set up a base station in relation to other stations. Manual programming of base stations is prone to errors and can be inaccurate if performed during a time when the various base stations are not utilized in a normal fashion (e.g., at 4:00 AM on a weekday). Further, programming base stations without taking into account a specific topography of an area may lead to incorrect (at times nonfunctional) results. If pico base stations are to become commonplace, a more efficient installation process is needed.
The above problems may be summarized as follows: 1) the inability to set up newly installed base stations automatically, 2) the loss of flexibility for installation of new base stations, and 3) the inability to coordinate handoff using primarily source and target base stations.